Thermally actuated arcuate strip type control device



Dec. 22, 9 R. VlCENZl ETAL THERMALLY ACTUATED ARCUATE STRIP T ZPE CONTROL DEVICE Filed Jan. 22, 1962 INVENTORS Reno L. \hcmm JOHN A. Kuzmfia E ATTORNEY United States Patent THERMALLY AtCTUATlED ARQUATE S'll'tlil TYPE @GNTRUL DEVICE Reno L. Vicenri and .lohn lifleinheinz, Riverside, (Ialifi, assignors to Controls Qoinpany of America, Schiller Park, Ill, a corporation of Delaware Filed Jan. 22, 19%, Ser. No. 167,573 '7 Claims. (@l. Nth-137) This invention relates to a flame or temperature responsive control of the type generally used to sense the presence or absence of a flame in order to control the flow of fuel to a burner.

Devices of this type generally fall into one of two types, the first being a rod enclosed within a tube and the secend being a strip mounted adjacent a rod or tube. The two elements in either type are interconnected at one point and are provided with different temperature coefficients of expansion so that differential movement be tween the two elements can be employed to effect a control function, generally the actuation of a switch. Both types are subject to fatigue and failure by reason of warpage of one or both of the elements. The rod and tube type is probably the more durable of the two but, on the other hand, is less responsive than the strip type.

The present invention relates to the strip type and has for an object the provision of a strip configuration which is highly resistant to warpage and consequent failure as found in the prior art while retaining the high speed response characteristics inherent in heating a thin strip of metal.

This invention more particularly pertains to controls of a type which are generally considered to be temperature responsive even though in practice they are frequently referred to as flame sensors. While the present con figuration can also be classified as temperature responsive it is proper to refer to it as being flame responsive in that, when installed in accordance with the design parameters, the control can be operative to sense a flame while under similar environment conditions it would be insensitive to temperature in the sense that if the temperature of both the strip and the rod are the same the device would be non-responsive. In other words, while we prefer to use materials having different temperature co-eflicients of expansion, it is feasible to employ materials having the same temperature co-efiicients and still have the device responsive to flame although it would obviously not respond to temperature since there would be no differential in movement.

Another object of this invention is to provide a construction which is easily calibrated and which will retain its calibration throughout its operational life. in doing this we have provided for direct actuation of the switch through an adjustable interconnection between the strip and the switch. This interconnection has a direct action on the switch rather than employing any levers or the like to multiply the motion. As a result there are no factors such as bearing wear to disturb calibration. The interconnection also permits a simple arrangement for preventing overloading the switch.

The novel features of this invention will be set forth in the appended claims. The invention itself, together with additional objects and advantages thereof, will be more clearly understood from a reading of the following description in connection with the accompanying drawings wherein a preferred embodiment of this invention is illustrated and in which:

FIG. 1 is a front elevation of the control mechanism partially in cross-section;

PEG. 2 is an end view of the mechanism; and

PEG. 3 is a cross-sectional view taken along lines 3-3 of FIG. 1.

EJhZQMZ Patented Dec. 22, 1964 With reference to the drawings, a mounting bracket in has a front web 12 which supports rod 14. A strip 16 has its outer end spot welded or otherwise connected to the outer end of rod 14. The inner end of strip 16 is connected to a sliding shaft 18 which has a square cross section and projects through a cooperating hole in the web which prevents twisting of the strip during calibration which will be described hereinafter. The inner end of this shaft carries a threaded stud 26 having a washer 22 mounted thereon to provide a shoulder against which a leaf spring 24 bears to preload the strip toward actuation. The ends of the leaf spring are anchored in corners provided by the inturned flanges 26 on the front web.

A spring bracket 28 is threadedly mounted on stud 29 and has one end of a U-shaped leaf spring 3t) riveted to portion 331 of the bracket. The other end of leaf spring 30 projects through an aperture 32 in portion 33 of the bracket to bear against a cross member 34 of portion 33. The force exerted by spring 34 is greater than the force required to operate switch 36 by means of its plunger 38. Therefore, spring 30 provides for direct transmission of actuating movement between strip 116 and the switch and, in the normal operating range of the switch, the spring will be in the position shown in FIG. 1 but if the strip should expand beyond the point at which the switch is actuated this overtravel is taken up by lifting spring 3% off cross piece 34 thereby preventing overload of the switch or distortion of the parts.

It should also be noted that, in addition to providing a direct connection between strip and switch, the combination spring and bracket provides for accurate and facile calibration. Bracket 28 can be rotated on stud Ztl to vary the position of spring 30 relative to plunger 33 while maintaining both the direct connection between strip and switch and the overtravel feature. The bracket and spring can be suitably fixed in a particular relative position to achieve a desired calibration and, since there will be virtually no wear of the spring and bracket, the original calibration will not be changed during usage.

Strip in has an arcaute configuration throughout the major portion of its length with the degree of curvature being selected so as to provide uniform spacing between the strip and the rod at any point where a cross-section .would be taken through both of them as for example,

in FIG. 3. This device is preferably arranged so that the flame impinges on the strip as indicated in FIGS. 2 and 3. Under these circumstances it will be apparent that rod 14 lies in the shadow of the strip and, hence, is not subjected to the direct heat of the flame. This provides uniform temperature across the rod and prevents Warping of the rod. The curvature of the strip accomplishes two purposes. A flat strip tends to concentrate the heat along the edges causing rippling of the edges and ultimate failure whereas the curved strip places the edges a little further from the flame and tends to equalize the temperaturesexisting across the strip. Furthermore, with the strip being generally uniformly spaced from the rod the strip can uniformly radiate heat to the rod. The result is that the strip exhibits no edge warping or distortion even after prolonged use.

in operation the flame will impinge on the strip as noted above and this will occasion the strip expanding at a very rapid rate as compared to the rate of expansion of the rod lying in the shadow of the strip. As the strip expands the loading spring 24 will move the threaded stud to the right carrying the switch actuating spring and its bracket to the right to actuate the switch through its plunger. in the usual situation switch as would be the normally open type which would be closed in response to the flame to establish a circuit permitting a fuel valve to open if the other parts of the control system so require. When the flame is extinguished the strip will cool off rapidly, because of its low mass, and will open the switch within a short period of time after flame failure.

To maximize the responsiveness of the control it is obvious that the co-eflicient of expansion of the strip should be higher than that of the rod. With this situation should the temperature of the rod tend to stabilize close to the temperature of the strip the difference in the coefficients will insure response of the control, such a control would be fully temperature responsive. t is possible to mount the actuator end of the strip in such a manner as to increase the spacing betweenthe strip and the rod and under these circumstances it is less likely that the strip and rod temperatureswill equalize. -It is also feasible to make the strip and rod of the same material and rely on the shadow effect, i.e. the rod being in the shadow of the strip, and the temperature'dilferential resulting from this to have a control that will respond to the flame whereas the control would not respond to temperature alone.

The discussion and description of this invention in connection with a particular preferred embodiment thereof has been for illustrative purposes only and should not be taken by way of limitation. Accordingly, it is intended in the appended claims to cover all modifications and embodiments of this invention as fall within the true spirit and scope thereof.

What we claim is:

1. A'control device adapted to respond to a flame or variation in temperature comprising, in combination, a frame, a switch supported on said frame, a rod fixed to said frame, a strip connected at one end to said rod and extending longitudinally of and in spaced relation to said rod, said strip being generally arcuate in transverse cross section and uniformly spaced fromsaid rod in any transverse plane through said rod and strip along the iongitudinal extensions thereof, said strip arranged exteriorly of and with its edges extending toward said rod, and means connected to the free end of said strip and engaging said switch for transmitting motion of said strip to said switch for actuation thereof.

2. A control device adapted to respond to a flame or a temperature variation comprising, control means, a generally elongated first member, a second member having a configuration conforming to said first member and positioned adjacent to and extending generally co-extensive with said first member, said second member disposed externally of said first member with its edges extending toward said first member and uniformly spaced from said first member in any transverse plane through said first and second members along the longitudinal extensions thereof, said fisrt and second members being interconnected with one of said members fixed relative to said control means so that in response to a temperature variation the other of said members moves relative tosaid control means, and means for connecting theother of said members to said control meansfor transmitting said motion to said control means for actuation thereof.

3. A control device adapted to respond to a heat source comprising, in combination, control means, first and second interconnected members exposed to said heat source, one of said members being fixed relative to said control means and the other of'said members being moveable relative thereto in response to exposure to said heat source, one of said members having a configuration conforming to that of the other of said members and arranged inembracing relationship with a portion of said other member with its edges extending away from said heat source and being uniformly spaced from said other member, and means connecting said movable member to said control means and transmitting movement of said moveable member to said control means for actuation thereof; and

f further characterized by said heat source being arranged exteriorly of said control device so that said control device can be arranged with said one member disposed intermediate said heat source and said other member.

4. A control device adapted to respond to a dame comprising, in combination, a frame, a switch supported on said frame, a rod fixed to said frame, a strip connected at one end to said rod and extending longitudinally of and in spaced relation to said rod, said strip being generally arcuate in transverse cross-section and uniformly spaced from said rod in any transverse plane through said rod and strip along the longitudinal extensions thereof, said strip arranged with the concave side thereof toward said rod and arranged in said control device so that saidcontrol device is adapted to be disposed with said strip intermediate said rod and flame, a threaded stud connected to the free end of said strip, a support member threadably engaging said stud and a spring mounted on said support member and engaging said switch, said spring being mounted to directly transmit motion of said strip to the switch and mounted to yield upon movement of said strip beyond that required for switch actuation.

5. The combination of claim 4 including spring means for preloading said strip inthe direction of actuation of said switch.

6. A control device adapted to respond to a heat source comprising, in combination, a frame, a switch supported on said frame, a rod fixed to said frame, a strip connected at one end to said rod and extending longitudinally of and in spaced relation to said rod, said strip beinggenerally arcuate in transverse cross-section anduniformly spaced from said rod in any transverse plane through said rod and strip along the longitudinal extensions thereof, said strip arranged with the concave side thereof toward said rod and arranged in said control device so that said control device is adapted to be disposed with said strip intermediate said rod and heat source, whereby said strip is movable in response toexposure to said heat source, and means connected to the free end of said strip and engaging said switch to transmit'the movement of said strip directly to said switch for actuation thereof, said last-mentioned means including spring means adapted to yield upon movement of said strip after actuation of said switch.

7. A control device adapted to respond to a heat source comprising, in combination, a frame, a switch supported on said frame, a rod fixed to said frame, a strip connected at one end to said rod and extending longitudinally of and in spaced relation to said rod, said strip being generally arcuate in transverse cross-section and uniformly spaced from said rod in any transverse plane through said rod and strip along the longitudinal extensions thereof, said strip arranged with the concave side thereof toward said rod and arranged in said control device so that said control device is adapted to be disposed with said strip intermediate said rod and heat source, whereby said strip is movable in response to exposure to said heat source, and means connected to said strip and engaging said switch for transmitting the motion of said strip to said switch for actuation thereof.

References .Cited in the file of this patent UNITED STATES PATENTS 2,426,786 Newell Sept. 2, 1947 2,494,660 Kathe Ian. 17, 1950 2,630,479 Villarreal Mar. 3, 1953 2,789,176 Mercier Apr. 16, 1957 2,990,716 Butts July 4, 1961 

1. A CONTROL DEVICE ADAPTED TO RESPOND TO A FLAME OR VARIATION IN TEMPERATURE COMPRISING, IN COMBINATION, A FRAME, A SWITCH SUPPORTED ON SAID FRAME, A ROD FIXED TO SAID FRAME, A STRIP CONNECTED AT ONE END TO SAID ROD AND EXTENDING LONGITUDINALLY OF AND IN SPACED RELATION TO SAID ROD, SAID STRIP BEING GENERALLY ARCUATE IN TRANSVERSE CROSS SECTION AND UNIFORMLY SPACED FROM SAID ROD IN ANY TRANSVERSE PLANE THROUGH SAID ROD AND STRIP ALONG THE LONGITUDINAL EXTENSIONS THEREOF, SAID STRIP ARRANGED EXTERIORLY OF AND WITH ITS EDGES EXTENDING TOWARD SAID ROD, AND MEANS CONNECTED TO THE FREE END OF SAID STRIP AND ENGAGING SAID SWITCH FOR TRANSMITTING MOTION OF SAID STRIP TO SAID SWITCH FOR ACTUATION THEREOF. 